1. Field of the Invention
The present invention relates to a high frequency semiconductor device housing package for mounting and housing therein a high frequency semiconductor device such as a high frequency semiconductor circuit device used in the microwave or millimeter wave region, the package being of the type generally known as a ball grid array package which is mounted on an external electrical circuit board via ball-shaped terminals. More particularly, the invention relates to a high frequency semiconductor device housing package that ensures high mounting yields, and that enhances the efficiency of high frequency signal transmission at ball-shaped signal terminal mounting pads to which the ball-shaped signal terminals are attached.
2. Description of the Related Art
An external electrical circuit board, such as a mounting board for mounting thereon a high frequency semiconductor device housing package with a high frequency semiconductor device housed therein, uses planar circuits such as microstrip lines as circuit interconnections on its surface. In particular, in cases where a high frequency semiconductor device housing package having a large number of ball-shaped terminals arranged in a grid pattern on the lower surface thereof, i.e., the so-called ball grid array package, is surface mounted on an external electrical circuit board, an interconnect structure in which grounding conductor layers such as coplanar microstrip lines are formed in the same plane as signal wiring conductors is advantageously used as the circuit interconnect structure on the external electrical circuit board, because it has good affinity from the viewpoint of package grounding.
The mounting of the high frequency semiconductor device housing package on the external electrical circuit board is completed as follows. Ball-shaped terminal mounting pads are formed at the ends of the signal wiring conductors of the mounting board having the above wiring structure, and are connected via ball-shaped signal terminals formed by solder or like material to the ball-shaped terminal mounting pads formed on the lower surface of the package. Then, the grounding conductor layers formed on the upper surface of the mounting board and the lower surface of the package in such a manner as to surround the ball-shaped terminal mounting pads are interconnected via ball-shaped grounding terminals, and the ball-shaped terminal mounting pads for a bias circuit are also interconnected via ball-shaped bias terminals.
The high frequency semiconductor device housing package described above not only can reduce the mounting area compared with conventional packages with external leads, but also can address the need for smaller package dimensions since the circuit interconnects within the package can be formed in multiple layers by using multilayer technology.
The high frequency semiconductor device housing package also has the advantage that when mounting the package using the ball-shaped terminals, the self alignment effect of the ball-shaped terminals ensures good mounting accuracy and provides excellent affinity for automation of the mounting work, as well as the advantage of high mass producibility offered by thick film printing and multiple dielectric layer deposition technologies.
However, the prior art high frequency semiconductor device housing package of the ball grid array type described above has had the problem that the ball-shaped terminal mounting pads consume large area compared with the fine signal wiring conductors, because there is a need to increase the bonding strength by increasing the size of the ball-shaped terminal mounting pads in order to enhance the mounting reliability of the ball-shaped terminals. That is, in the case of a distributed constant circuit used in the microwave or millimeter wave band, in particular, if there is a wide line portion in a circuit interconnect, the capacitance formed at that portion increases, increasing parasitic capacitance and decreasing the characteristic impedance of the circuit interconnect, resulting in increased reflections of the high frequency signal due to impedance mismatch; hence, the prior art has had the problem that as the frequency of the signal increases, transmission of the signal becomes increasingly difficult.
The present invention has been devised in view of the above problem associated with the prior art, and an object of the invention is to provide a high frequency semiconductor device housing package whose ball-shaped signal terminal mounting pads have good high frequency signal transmission characteristics at microwave or millimeter wave frequency, without losing the benefits of a ball grid array package, such as high mounting accuracy and excellent affinity for mounting work automation, reduced mounting area and package dimensions, and high mass producibility of thick film printing and multiple dielectric layer deposition technologies.
The invention provides a high frequency semiconductor device housing package, comprising:
a dielectric substrate fabricated by stacking a plurality of dielectric layers one on top of another, the dielectric substrate having, on its one surface, a mounting and housing portion for mounting and housing therein a high frequency semiconductor device;
an internal signal wiring conductor formed within the dielectric substrate so as to extend from the mounting and housing portion through another surface of the dielectric substrate opposite to the one surface, to which an electrode of the high frequency semiconductor device is electrically connected;
an interlayer grounding conductor layer formed between the dielectric layers;
a signal wiring conductor formed on the other surface of the dielectric substrate so as to be opposed to the interlayer grounding conductor layer, the signal wiring conductor being electrically connected to the internal signal wiring conductor;
a ball-shaped signal terminal mounting pad provided on a tip of the signal wiring conductor; and
a grounding conductor layer formed in such a manner as to surround the signal wiring conductor and the ball-shaped signal terminal mounting pad,
wherein, in the interlayer grounding conductor layer opposed to the signal wiring conductor is provided a conductive layer non-forming portion so as to be located in a region directly above the ball-shaped signal terminal mounting pad,
and wherein an effective distance from the ball-shaped signal terminal mounting pad to the interlayer grounding conductor layer is made greater than an effective distance from the ball-shaped signal terminal mounting pad to the grounding conductor layer.
According to the invention, the internal ground conductor layer, disposed opposite the signal wiring conductor formed on a lower surface, i.e. the other surface of the dielectric substrate, is provided with a conductor layer non-forming portion in the region directly above the ball-shaped signal terminal mounting pad formed on the tip portion of the signal wiring conductor on the lower surface, and the effective distance from the ball-shaped signal terminal mounting pad to the interlayer grounding conductor layer is thus made greater than the effective distance from the ball-shaped signal terminal mounting pad to the conductor layer that is formed on the lower surface in such a manner as to surround the ball-shaped signal terminal mounting pad; with this configuration, the capacitance formed between the ball-shaped signal terminal mounting pad and the interlayer grounding conductor layer directly above it can be held to a low value. Thus, the parasitic capacitance at the interconnection between the transmission line on the upper surface of the external electrical circuit board, to which the ball-shaped signal terminal mounting pad is connected via a ball-shaped signal terminal, and the transmission line on the lower surface of the package, of which the ball-shaped signal terminal mounting pad is a part, can be reduced, so that signals up to the high frequency regions of microwave or millimeter wave frequency can be efficiently passed through the ball-shaped signal terminal mounting pad.
According to the invention, it becomes possible to provide a high frequency semiconductor device housing package whose ball-shaped signal terminal mounting pads have good high frequency signal transmission characteristics at microwave or millimeter wave frequency, without losing the benefits of a ball grid array package, such as high mounting accuracy and excellent affinity for mounting work automation, reduced mounting area and package dimensions, and high mass producibility of thick film printing and multiple dielectric layer deposition technologies.
In the invention, it is preferable that through-hole conductors for electrically connecting the grounding conductor layer with the interlayer grounding conductor layer by passing through the dielectric layers are formed around the conductor layer non-forming portion at intervals not larger than one quarter of a guide wavelength of a high frequency signal.
In the invention, it is preferable that ball-shaped grounding terminals for physically and electrically connecting the grounding conductor layer with a grounding conductor on an external electric circuit board are formed in the grounding conductor layer around the ball-shaped signal terminal mounting pad at intervals not larger than one quarter of a signal wavelength of a high frequency signal.